Laser diodes and light-emitting diodes suitable for optical communication systems have reached a stage of maturity which makes their practical use possible. Of the two spectral regions of interest, 0.8 to 0.9 μm and 1.1 to 1.7 μm, the first is the most widely used because the AlGaAs double heterojunction devices are the most developed. However, rapid progress is being made in the development of the longer wavelength InGaAsP/InP devices. Laser research and development is currently also focused on devices operating reliably in the fundamental spatial mode in order to insure kink-free operation and a single beam far field. Several structures have been developed which meet the objective of fundamental spatial mode operation at power levels (cw) on the order of 10 mW.